I am not doing SQL-Updates (yet), but I am taking a DBC, creating a table from scratch, altering it, and inserting a little over one million rows in a VBScript file. Here's an excerpt of relevant code from my spaghetti:

Set oCacheConn = CreateObject("ADODB.Connection")
With oCacheConn
  .ConnectionString = "Provider=VFPOLEDB.1;Data Source=" & cCacheDir & cDestDB
  .CursorLocation = 2 ' adUseServer
  .Mode = 16 ' adModeShareDenyNone
  .Open
End With
cExec = "Alter Table " & cVFPTable & " Add Column " & cNuColName & " " & cColType & "(" & cColWidth & ")"
oCacheConn.Execute(cExec)
cExec = "Insert Into " & cVFPTable & " (" & cColSpec & ") Values (" & cVals & ")"	'WScript.Echo cExec
oCacheConn.Execute(cExec)

This is running fine for me every day. I don't see why an update would fail if insert is working, but you never know. I don't use recordsets when querying (I use GetRows() into an array) or updating (I would build an insert string), so maybe that is why I am not seeing issues that others do.

HTH.